This invention relates to display devices, and particularly to display devices employing liquid crystal light scattering means.
Display devices employing liquid crystal light scattering means are known, and are described, for example, in U.S. Pats. No. 3,322,485, issued to R. Williams, on May 30, 1967, and 3,499,112, issued to Heilmeier et al., on Mar. 3, 1970. In these devices, a light scattering means, such as a nematic liquid crystal compound, is used which has the property of being either substantially transparent to light in one state, or being forward scattering of light in another state, the states being reversibly switchable.
One type of liquid crystal device comprises a pair of transparent substrates, a liquid crystal material sandwiched between the substrates, and conductive transparent electrodes on the inside surfaces of the substrates. In order to efficiently utilize the forward scattering characteristic of the liquid crystal material, the device is disposed between a source of illumination and the viewer. This arrangement provides bright displays and high contrast ratios between various portions of the displays.
A problem with this arrangement, however, when the device is disposed directly between the viewer and the light source, is that the light source is visible to the viewer when the liquid crystal material is in its transparent state. In some instances, this can be disturbing.
In another application, the light source is disposed out of the line of sight of the viewer. A disadvantage of this arrangement, however, is that it is somewhat difficult to provide uniform and efficient lighting of the device while providing devices of comparatively small size.